Skin packaging can be classified as a vacuum forming process for thermoformable polymeric films. However, the term "vacuum skin packaging" or VSP as it is referred to hereinafter, refers not to the fact that the thermoformable film is formed around the product by vacuum or differential air pressure which, indeed it is, but more to the fact that the product is packaged under vacuum and the space containing the product is evacuated. Thus, in VSP processes the film formed around the product must be a barrier to oxygen, air, and other gases. However, in conventional skin packaging, a backing board which is porus or which is perforated so that a vacuum may be drawn directly through the backing board is employed.
In VSP processes, generally a vacuum chamber with an open top is used. The product on an impervious backing board is placed on a platform within the vacuum chamber. The top of the chamber is covered by a sheet of film which is clamped tightly against the chamber to form a vacuum tight closure. The chamber is evacuated while the film is heated to its forming and softening temperature. The platform is then raised to drive the product into the softened film and air pressure is used above the film to force it tightly around the product. A similar type process is disclosed in French Pat. No. 1,258,357 which issued to Alain G. Bresson on Mar. 6, 1961.
A variant of the process described in the Bresson patent is disclosed in French Pat. No. 1,286,018 which issued on Jan. 22, 1962 to LaRoach Freres Limited. The LaRoach Freres process, after the chamber has been evacuated and the product driven into the heat softened film, the vacuum is released and ambient air is permitted to enter the chamber so that the thermoplastic film molds more or less onto the product since there is a vacuum on the product side of the film and ambient air pressure on the other side of the film. Australian Pat. No. 245,774 which issued to Colbros Proprietary Limited et al on July 16, 1967 discloses a vacuum skin packaging process in which an article to be packaged is inserted within the lower half of a vacuum chamber on a backing board, a thermoplastic film is placed over the opened face of the lower half of the chamber, the chamber is closed and both halves and are brought to essentially the same state of vacuum, the film is heated and softened, and, then, atmospheric air is introduced into the upper half of the chamber so that it alone forces the thermoplastic film down around the product and against the backing board. Another version of vacuum skin packaging is disclosed in U.S. Pat. No. 3,491,504 which issued to W. E. Young et al on Jan. 27, 1970. In this version, heat softened film with equal vacuum on both sides thereof is physically moved down over a stationary product or the product moved into the film and, when air pressure is increased on the outside of the film, the softened thermoplastic film is molded onto the product.
In U.S. Pat. No. RE. 30,009, which was reissued on May 29, 1979 to Richard R. Perdue et al, a process and package is disclosed wherein a thermoformable or heat softenable film sheet is drawn by differential air pressure against the concave interior surface of the upper portion of a vacuum chamber, the film is then heated by surface contact, and then, after evacuation of the chamber, air pressure is used to blow the film down over product positioned on an impervious backing board. The resulting package comprises the product held on the backing board by the thermoformable film which has been formed around the product in the exact shape of the product so that it appears to be a "skin." The thermoformable film, as stated previously, is also gas impervious and usually will consist of a number of layers each of which performs a specific function. The product contact and backing member contact layer will be a sealing or heat sealable layer. The interior layer will typically be a barrier layer which comprises a vinylidene chloride copolymer or a hydrolyzed ethylene/vinyl-acetate copolymer; and, an outer surface layer will be provided to protect the barrier layer from scratches, pin holes or other abuse and from moisture attack. Usually the package surface will not be particularly smooth or uniform as the surface conforms to the shape of the product. Accordingly, one general object of the present invention is to provide a satisfactory method of labelling vacuum skin package which conform to the product shape.
In U.S. Pat. No. 3,574,642 which issued on Apr. 13, 1971 to Carl Frederick Weinke. A package for a method of packaging meats is disclosed. The package includes an inner oxygen-permeable member which may be either gas flushed or evacuated and an outer oxygen-impermeable member which may also be gas flushed or evacuated. The package preserves the freshness of the meat until the meat is ready to be marketed to the consumer but the meat is purplish in color. For marketing, the outer wrapper is removed and the inner package is displayed to the consumer. Being oxygen-permeable, the inner wrapper admits oxygen to the interior of the package causing the fresh meat product to change to a bright red color which the consumer associates with freshness. The inner pouch of the Weinke package may consist of polyethylene film and the outer pouches may be cellophane film with a coating of saran (vinylidene chloride copolymer). Another patent showing portions of fresh meat individually packaged in oxygen permeable plastic film and inserted into a outer container of impermeable film is U.S. Pat. No. 3,681,092 which issued to Oliver R. Technell et al on Aug. 1, 1972.
A prior art package of interest is described in U.S. Pat. No. 3,713,849 which issued to Paul E. Grindrod et al on Jan. 30, 1973. In the Grindrod et al patent a fresh meat package having an outer oxygen impermeable layer which is readily and entirely peelable from an inner oxygen-permeable layer is disclosed. The package includes means for initiating the peeling separation along an edge of the package. The outer oxygen barrier maintains meats in well preserved condition the purplish color which has low consumer appeal. Shortly prior to display for sale to the consumer the outer layer is removed by the retailer and the product develops healthy, bright red "bloom" due to the high oxygen penetration of the remaining inner film package. The materials disclosed in Grindrod et al are laminates of PVC/Saran and EVA/Saran. (EVA designates ethylene/vinyl-acetate copolymer and PVC designates polyvinyl-chloride.) The EVA and PVC layers are the inner layers and at the periphery of the package they are sealed together. The saran layers can be readily peeled from the respective EVA or PVC layers and gripping tabs are provided for initiating the peeling process.
Yet another peelable package is shown in U.S. Pat. No. 4,055,672 which issued on Oct. 25, 1977 to Arthur Hirsch et al. In the Hirsch et al patent, a semi-rigid preformed tray of oxygen impermeable material is formed, a meat product placed therein and then the tray is sealed around its upper peripheral or flange area by a composite lid which has an inner layer of oxygen impermeable material, an adhesive layer, and an outer layer of oxygen impermeable material. When the package is ready for retail displays so that oxygen can reach the fresh meat package within the tray, the outer, impermeable lid is peeled away so that the oxygen can penetrate through the remaining portion of the lid. Accordingly, another object of the present invention is to provide a package with a strippable or peelable barrier layer which has a label which is not moved or displaced by the peeling process.
In order to readily open packages where plastic film layers have been sealed together to close the package, various tear tabs and easy open mechanisms have been devised. One such easy open, delaminating seal is disclosed in U.S. Pat. No. 4,638,913 which issued on Jan. 27, 1987 to Milton A. Howe, Jr. In this disclosure, two grippable film folds are provided and the folds, when pulled apart, will rupture one of the outer layers of the sealed together film and delaminate the film to its edge. In such a case, of course, the bond strength between the two sealed together films must be greater than the layer to layer bond of the film. Accordingly, it is still another object of the invention to provide a package which it is readily openable without removing or displacing the label for the package. In the prior art it has been known to seal a label between two layers of thermoplastic material to protect the label or to separate the label from the contents of the package. Such a label sealing method is shown in U.S. Pat. No. 3,638,784 which issued on Feb. 1, 1972. However, positioning the label a separate compartment or separating it by an additional film member means higher costs in both film and labor. Accordingly, it is one object of the present invention to provide a simplified method of providing a label which is sealed internally in the package.
In the prior art, when labels are placed inside a package, these labels can be displaced or moved within the package as it moves through the handling and distribution chain. Accordingly, it is another object of the present invention to provide an internal label which minimizes the chances that it will move from its original location.
When packaging foods which may exude fluids such as fresh red meat will, if a label is placed on the inside of the package it will tend to become discolored and in some cases unreadable due to the migration of the fluids over the visible label area. Accordingly, it is yet another object of the present invention to provide a label which will not be rendered illegible by the presence of fluids within the package.
When cold, wet surfaces are to be labeled as is the case when meat wrapped in plastic film for showcase display is to be labeled, it is often difficult to get the label to stick to the surface of the film by any quick means as the surface is soft and spongy and label adhesives sometimes tend to resist sticking to a moist, cold surface. Often, such labels will come off the package or become unreadable because of the crush and abuse from adjacent packages in transportation, storage, or display. Accordingly, it is still another object of the present invention to provide a label which will remain with the package and continue to be legible throughout the handling and display process.
These and other objects and the accomplishment thereof will become apparent to those skilled in the art from the following Summary of Invention, Description of the Drawings, and Detailed Description.